Is there any way to filter manga based on how many people have it on their wish list?
And maybe filter it further to the ones that are complete but not completely scanlated?

A friend of mine wants to start (another) group that focuses on dropped series that are at least kinda popular or something, and I thought this might help him.

Thanks for your time!

This thread may help out your friend ... But to my knowledge I don't know of such a feature. ( the seeing what's popular on wish lists.)

Yes yes, I know I make longwinded comments, but that's just me >.<
I should proof read my comments more, but I won't...
So keep in mind I'm filled with typos

Check out FAQ and Forum Rules if you haven't yet.
For errors linking in threads

There's this for the first part of your request, but I don't think the 2nd part can be done at present, so your friend would have to open each one manually to look whether they have been completed/completely scanlated or not.

世界のどこかに必ず
キミの居場所がある筈

Ooh. Those are very helpful. I'll refer these to my friend. Thank you very much ^_^